One hundred patients have been entered in a prospective, randomized study comparing medical and surgical therapy for chronic, stable, disabling angina pectoris. New entries to the study were closed in early 1977 at the end of the initial 5-year period. All patients undergo coronary arteriography, left ventriculography, myocardial metabolic study, graded exercise stress testing and evaluation of risk factors initially, 6 months after entry and after 5 years. All patients were in Functional Class III at the time of entry and initial clinical and angiographic data are similar in the medical and surgical groups. Mean followup time in the 49 medical and 51 surgical patients is 40 months. Major cardiac events requiring termination from the study are as follows: death (all cardiac)--5 in medical and 4 in surgical patients; myocardial infarction--8 in medical and 10 in surgical patients; high risk unstable angina requiring operation--8 medical and 3 surgical patients. In addition, 7 medical and 3 surgical patients developed unstable angina which subsided with medical treatment. There is no significant difference in overall terminating events between the two groups but there is a significant difference (p is less than 0.02) in terminating events in patients with three vessel disease. This is due primarily to the higher incidence of high risk unstable angina in medical patients (p is less than 0.02). There was a significantly greater improvement in Functional Classification in surgical patients at the time of 6 months followup (p is less than 0.01) and this has been sustained at the time of latest followup averaging 40 months (p is less than 0.05). This symptomatic improvement has been corroborated by exercise stress testing which demonstrates an initial and continued improvement in surgical patients and a small but significant deterioration in medical patients in both maximum work load and maximum heart rate achieved. There were no significant differences in left ventricular function as judged by ejection fraction and end diastolic pressure in either group or between the two groups.